JP2011010336A - Method and system for performing handoff in wireless communication system, such as hard handoff - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method and system for providing hard handoffs between high-speed cells.SOLUTION: A mobile station transmits a plurality of channels including a pilot channel and at least one information channel. A base station determines the adequacy of the transmission energy of a reverse link signal in accordance with received energy of a reverse link pilot signal. Pilot channel transmission power is retained at a level prior to a frequency search excursion, while increasing the transmission energy of at least one other channel transmitted by the mobile station. In addition, when the mobile station is not capable of increasing the transmission energy of all of the information channels, the mobile station generates a ranking of the importance of the different information channels and selectively increases the transmission power of those channels.

Description

Detailed Description of the Invention

  The present invention relates to wireless communication systems, and more particularly to a method and apparatus for providing hard handoff between cells of such a system.

Conventional technology

  In code division multiple access (CDMA) systems, most handoffs occur between cells on the same CDMA channel and use a soft handoff procedure. In some cases, the mobile station needs to perform a handoff between cells on different CDMA channels. In this case, such channels differ in radio frequency (FR) and are often referred to as inter-frequency hard handoff. Such situations are typically handoffs between different operators, handoffs between different RF channels assigned for capacity reasons, or handoffs between different signal modulation techniques, but are not limited thereto. Absent.

  Prior to performing an inter-frequency hard handoff, the mobile station is directed to tune to a new target frequency by the base station, measure the radio environment (eg, pilot signal strength, eg, received signal), and return the measurement to the base station. . Such a procedure is specified in TIA / EIA-95-B and greatly increases the probability of successful inter-frequency handoff.

  An essential requirement for measurements on the target frequency, often referred to as “search excursion”, is to minimize disruption of the current service on the starting frequency. The second without appropriate pre-sampling. A handoff to a frequency of 2 may result in degraded signal performance, while long-time sampling may completely lose the signal at the first frequency, which is a method that allows the mobile station to minimize search time. And make it possible to limit disruption of service.

  The mobile station transmits a plurality of channels including a pilot channel and at least one information channel. In the exemplary embodiment, the base station determines the appropriateness of the reverse link signal transmission energy according to the received energy of the reverse link pilot signal. In the present invention, the transmission power of the pilot channel is maintained at the level before the frequency search excursion while increasing the transmission energy of at least one other channel transmitted by the mobile station. Furthermore, when the mobile station is unable to increase all the transmission energy of the information channels, the mobile station generates a ranking of the importance of the different information channels and selectively increases the transmission power of these channels.

1 is a diagram showing a typical wireless communication system to which the present invention can be applied. FIG. 2 is a block diagram of exemplary components found in the wireless communication system of FIG. 1 to which the present invention can be applied. It is a timing diagram of the search excursion between frequencies. 4 is a flowchart of a method for performing frequency search excursion in an embodiment of the present invention. FIG. 6 is a power versus time graph showing transitions in the forward link power level associated with an inter-frequency search excursion. FIG. 6 is a power versus time graph showing reverse link power increase during search excursion. FIG. 6 is a flowchart of a method for performing frequency search excursion while minimizing service interruption according to another embodiment of the present invention; FIG. 2 shows a multi-channel remote station of the present invention. FIG. 3 shows a reverse link modulator of the present invention.

In the figure, the same parts are denoted by the same reference numerals. To make it easier to see the description of a particular element, the most significant digit of the reference sign indicates the figure number in which that element first appears. (For example, element 204 is first introduced and described in FIG. 2).
Details of the method and apparatus for minimizing search excursion time for the target frequency and disruption of current service on the starting frequency will now be described. In the following description, numerous specific details are provided to provide a thorough understanding of the present invention. However, one skilled in the relevant arts will readily recognize that the present invention may be practiced without these specific details or with other elements or steps. In other instances, well-known structures and methods are not shown in detail in order to avoid obscuring the present invention.

  FIG. 1 shows a cellular subscriber communications system 100 that uses multiple access techniques, such as code division multiple access (CDMA), to communicate between a user of a user station (eg, a mobile phone) and a cell site or base station. . In FIG. 1, a mobile user station 102 communicates with a base station controller 104 by one or more base stations 106a, 106b, etc. Similarly, fixed user station 108 communicates with base station controller 104 only by one or more predetermined and approximate base stations, such as base stations 106a and 106b.

  Base station controller 104 is connected to and generally includes an interface and processing circuitry for providing system control to base stations 106a and 106b. The base station controller 104 can be connected to and communicate with other base stations or other base station controllers. Base station controller 104 is connected to mobile switching center 110, which is connected to home location register 112. As is known in the art, during registration of each user station in the first part of each call, the base station controller 104 and the mobile switching center 110 include a registration signal received from the user station in the home location register 112. Compare the data with As is known by those skilled in the art, handoffs can also occur between the base station controller 104 and other base station controllers and between the mobile switching center 110 and other mobile switching centers.

  When the system 100 handles voice or data traffic calls, the base station controller 104 establishes, maintains and terminates radio links with the mobile station 102 and fixed station 108 while the mobile switching center 110 is a public switched telephone network. Establish, maintain and terminate communication with (PSTN). The following description focuses on signals transmitted between the base station 106a and the mobile station 102, but those skilled in the art will apply this description equally to other base stations and fixed stations 108. You will recognize that. Here, “cell” and “base station” are generally used alternately.

  Referring to FIG. 2, the mobile station 102 includes an antenna 202 that transmits signals to the base station 106a and receives signals from the base station 106a. The duplexer 203 supplies the forward link channel or signal from the base station to the mobile reception system 204. The reception system 204 down-converts, demodulates, and decodes the received signal. Next, the reception system 204 supplies predetermined parameters or parameter groups to the quality measurement circuit 206. Examples of parameters may include decoder parameters such as measured signal-to-noise ratio (SNR), measured received power, or symbol error rate, Yamamoto metric or parity bit check indication. A memory buffer 207 may be included for use with the invention described herein. Further details regarding the operation of mobile station 102 (and base station 106a) can be found, for example, in US Pat. No. 5,751,725 (invention title) assigned to the assignee of the present invention and incorporated herein by reference. : "Method and apparatus for determining the rate of received data in a variable rate communication system").

The quality measurement circuit 206 receives parameters from the reception system 204 and determines the power level of the quality measurement signal or the received signal. The quality measurement circuit 206 can generate an energy per bit (E _b ) measurement and an energy per symbol (E _s ) measurement from a portion or window of each frame. As is known in the art, preferably the energy measurement per bit or energy measurement per symbol is normalized (eg E _b / N _o ) or normalized interference factor (eg E _b / N _t ). Based on these measurements, the quality measurement circuit 206 generates a power level signal.

  The power control processor 208 receives the power level signal from the quality measurement circuit 206, compares the signal to a threshold value, and generates a power control message based on the comparison. Each power control message may indicate a change in power for the forward link signal. Alternatively, as known in the art, a power control message is generated that represents the absolute power of the received forward link signal. The power control processor 208 desirably generates several (eg, sixteen) power control messages in response to several power level signals per frame. Although the quality measurement circuit 206 and the power control processor 208 are generally described herein as separate components, such components can be monolithically integrated or the operations performed by such components can be performed by a single micro. It can be executed by a processor.

  Mobile transmission system 210 encodes, modulates, amplifies, and upconverts power control messages via duplexer 203 and antenna 202. In the illustrated embodiment, the mobile transmission system 210 provides a power control message at a predetermined location in the outgoing reverse link frame.

  The mobile transmission system 210 also receives reverse link traffic data, such as voice or general computer data, from mobile station users. The mobile transmission system 210 requests a specific service including (power / rate) from the base station 106a based on the traffic data to be transmitted. In particular, the mobile transmission system 210 requests bandwidth allocation appropriate for a particular service. If the system is power limited, the base station 106a plans or allocates bandwidth (power / rate) resources based on requests from the mobile station 102 and other users and optimizes the allocation of such resources. . Therefore, by efficiently managing the transmission power of the system, a more efficient band can be used.

  Base station 106 a includes a receive antenna 230 that receives reverse link frames from mobile station 102. The receiver system 232 of the base station 106a downconverts, amplifies, demodulates and decodes the reverse link traffic. The bypass relay transceiver 233 receives the reverse link traffic and sends it to the base station controller 104. Receiver system 232 also separates the power control message from each reverse link traffic frame and provides the power control message to power control processor 234.

  The power control processor 234 monitors the power control message and outputs a forward link transmitter power signal to the forward link transmitter system 236. In response, forward link transmission system 236 increases, maintains or decreases the power of the forward link signal. The forward link signal is then transmitted via transmit antenna 238. In addition, the power control processor 234 analyzes the quality of the reverse link signal from the mobile station 102 and provides an appropriate feedback control message to the forward link transmitter system 236. In response, forward link transmitter system 236 transmits a feedback control message to mobile station 102 via transmit antenna 238 and the forward link channel. Transmitter system 236 also receives forward link traffic data from base station controller 104 via backhaul transceiver 233. Forward link transmitter system 236 encodes, modulates, and transmits forward link traffic data via antenna 238.

  Unless otherwise noted herein, the various blocks and elements shown in FIGS. 1, 2 and other figures are generally designed and operated. Accordingly, such blocks and elements will be understood by those skilled in the art and need not be described in detail. Further description has been omitted for the sake of brevity and to avoid obscuring the detailed description of the invention. Variations required for the blocks of the communication system 100 of FIGS. 1 and 2 or other systems shown therein can be readily made by those skilled in the art based on the detailed description provided herein.

  A closed loop power control system for user stations, including mobile station 102 and base station 106a, dynamically adjusts transmit power for each user based on user propagation conditions and is the same for each user for voice service. A frame error rate (FER) is generated (eg, 1% FER). However, as mentioned above, many users may require transmission for data services instead of voice services, such as facsimile, email, and general computer data. All of these data are insensitive to delay and require lower FER (ie, low bit error rate (BER)). Users may request video services that are insensitive to delay as well as lower FER. The base station 106a dynamically assigns a transmission rate based on a request from each user under a known technique.

  According to one CDMA standard described in the Telecommunications Industry Association's "Mobile Station-Base Station Compatibility Standard for TIA / EIA-95-A Dual Mode Wide Spread Spectrum Cellular System", each base station is pilot, synchronous, Send paging and forward traffic channels to the user. The pilot channel is an unmodulated direct sequence spread spectrum signal transmitted continuously by each base station. The pilot channel allows each user to acquire the timing of the channel transmitted by the base station and provides a phase reference for coherent demodulation. The pilot channel also provides a means for signal strength comparison between base stations and determines when to handoff between base stations (as when moving between cells). Recently, CDMA modulation techniques using dedicated time multiplexed ("DTMP") pilot symbols have been proposed. In the DTMP approach, independent pilot symbols are time multiplexed on each user's traffic channel. Each user sequentially despreads pilot symbols (and information symbols). There are other common code multiplexed pilot ("CCMP") techniques. In this approach, one identical channel is used exclusively for broadcasting pilot signals. The pilot symbols are not multiplexed with the dedicated channel, and all users de-spread the pilot symbols and the modulation information signal in parallel. Such a system uses US patent application Ser. No. 09 / 144,402 filed Aug. 31, 1998, assigned to the same assignee of the present invention (Title of Invention: “Uses Inserted Pilot Symbols”). Methods and apparatus for reducing amplitude variations and interference in communication signals such as wireless communication signals ”).

Inter-Frequency Search Referring now to FIG. 3, a diagram of the different timings involved in performing a search excursion is shown. Although FIG. 3 is obvious to those skilled in the art, a brief description is provided. The reference symbol t _search corresponds to the time required to collect N samples at the frequency f2. The total time will be t _search plus the time taken to process the sample after returning to the original frequency f1. Times t _synth and t _settle correspond to the time required to switch and stabilize at the new frequency, respectively. The time period of Ns × Tc represents the sampling time of N _samples , and t _process represents the time for processing the samples.

  A method for minimizing the search time to another frequency can be described as follows.

  First, the mobile station is currently demodulating the original or first frequency f1. An inter-frequency hard handoff to the target frequency f2 may be required, such as when a certain signal quality measurement (eg, the measurement described above) is below a predetermined threshold. Upon reporting such degraded quality to the base station 106a, the mobile station 102 performs a search excursion to the target frequency f2 by the base station (eg, via a candidate frequency search request / control message (“CFSCM”)). You are instructed to do so.

  The mobile station tunes to frequency f2 and collects N-chip samples (1 chip is 1-bit pseudo-noise, for example at 1024 bps for orthogonally encoded symbols). Samples are stored in a memory buffer. The mobile station does not perform pilot search and pilot strength measurement while operating at the frequency f2. The mobile station returns to the original frequency f1, resumes reception on the forward link and transmission on the reverse link, and simultaneously processes the N samples collected at frequency f2.

  The mobile station processes samples collected at frequency f2 using a searcher that processes stored samples while simultaneously processing signals received at original frequency f1. The mobile station reports the corresponding pilot strength measurement from the frequency f2 to the base station. Those skilled in the art will recognize the searcher and have the necessary skills to provide or obtain the searcher.

  The method includes a routine beginning at step 410 where the base station 106a transmits a frequency change command to the mobile station 102 based on a candidate frequency search request control message defined by the TIA / EIA-95-B standard incorporated by reference. It is shown in FIG. In response to this command, the mobile station 102 tunes to the target frequency in step 420.

  In step 430, the mobile station 102 collects signal samples at the target frequency f 2 and stores the samples locally in the memory buffer 207. In step 440, the mobile station 102 retunes to the first frequency f1, and in step 450, processes the signal samples stored in the memory buffer 207. Steps 440 and 450 can be performed simultaneously.

  As described above, after the signal samples are processed, the mobile station 102 transmits the signal sample processing results to the base station 106a in step 460.

Minimizing the impact of search excursion on the current frame When the mobile station tunes to another frequency f2 to perform an inter-frequency search, the forward link symbol transmitted by the base station during the t _search time period is It cannot be received by the mobile station. In order to minimize the impact of this loss on the current forward link frame and reverse link frame, mobile stations and base stations are forward error correction coded for symbols that have been adversely affected by search excursion. , Increase the amount of power allocated to other symbols in the interleaved frame. In order for the frame to be correctly demodulated, the additional power required for a symbol that is not adversely affected by the search excursion is a function of the _search excursion time t _search as described herein.

Forward link power control during search patrol
To overcome the loss of the forward link symbol during the t _search time period, the mobile station increases the target Eb / No of the forward link closed loop fast power control by Δ _target dB.

This new target Eb / No is set in the K power control groups (PCG) before the search excursion. The required number K of the previous PCG is affected before the search excursion, and the required increase in the _target Eb / No (Δ _target ) depends on the period of the _search excursion t _search . The longer the t _search, K increases. As a result of the increase in target Eb / No, the forward link power will rise before the inter-frequency search.

  FIG. 5 shows a forward link level transition associated with an inter-frequency search excursion. FIG. 5 is obvious to those skilled in the art, but a brief description will be given. After the search excursion, the mobile station 102 resumes demodulating the forward link symbols of the current frame. At this stage, the mobile station 102 can know the total symbol energy received in the current frame and compare it with the required energy per frame to obtain the target frame error rate. The mobile station 102 uses this metric to increase or decrease the target Eb / No for the remaining power control group of the frame. As the search excursion extends beyond the frame boundary, the mobile station 102 can increase its target Eb / No in the next frame period to make up for the missing symbols in the first part of the frame. . For details on closed-loop power control, see US application Ser. No. 08 / 752,860, assigned to the assignee of the present invention and filed on November 20, 1996 (invention name: “predict power control commands not yet executed” Method and apparatus for adjusting thresholds and measurements of received signals ”and US application Ser. No. 08 / 879,274 filed Jun. 20, 1997 (Title:“ Power Adaptation ”) Method and apparatus for control and closed loop communication ").

Reverse link power control during a search cycle During a search for the target frequency f2, the base station 106 _loses communication with the mobile station 102 and does not receive a symbol for a t _search time period. To overcome these symbol losses, the mobile station 102 can increase the total transmit power on the reverse link by an amount Δsearch dB. The quantity Δsearch depends on the duration of the search t _search and overcomes the loss of symbols during the t _search period and adds to the additional required symbol energy for the remainder of the frame to allow the base station 106a to correctly demodulate the frame. Equivalent to. The base station 106a can inform the mobile station 102 of the maximum allowable increment Δsearch for a message that instructs the mobile station to perform an inter-frequency search (eg, in “FCSM”). This value may depend on the maximum allowable interference currently determined by the base station 106a.

  FIG. 6 shows the reverse link power increment transition during the search excursion. FIG. 6 is obvious to those skilled in the art, but will be described briefly. During an inter-frequency search frame period transmitted with a certain power increment, the base station 106a transmits a down command instructing the mobile station to reduce its power. The mobile station 102 simply ignores these down commands until the end of the inter-frequency search frame as shown in FIG. These up and down commands are represented in FIG. 6 by large black arrows 602 and 604, respectively. When the search excursion extends beyond the frame boundary, the mobile station 102 increases its total transmit power during the next frame in a manner similar to that described above to overcome the loss of the first symbol of the next frame. Can be increased. Normal power control resumes after the frame boundary as shown in FIG.

  Accordingly, the method described above in connection with FIG. 4 can be modified to ensure that communication is not blocked during the search excursion. FIG. 7 shows the modified method steps starting at step 710 where the base station 106 sends a frequency change command (FCSM) to the mobile station 102.

Before the mobile station 102 tunes to the target frequency, the target value Eb / No of the forward link closed loop high speed power control increases from the first level to the second level as described above. As described above and shown in step 720, the mobile station 102 increases the total reverse link transmission power by an amount Δ _search dB.

  Next, in steps 730 and 740, the mobile station tunes to the target frequency, collects target frequency signal samples, such as chip sample data, and stores the signal samples in memory 207.

  In step 750, when the collection of signal samples is complete, the mobile station 102 returns to tuning to the first frequency. The mobile station 102 processes the signal samples in the memory buffer and resumes communication with the base station 106a at the first frequency f1. As shown in step 760, when resuming communication, the mobile station 102 adjusts the target value Eb / No of the remaining power control groups in the frame, decreases the target value EB / No by Δtarget, and vice versa. The directional link total transmit power resumes normal control.

  Finally, in step 770, signal sample processing results, such as pilot strength measurements, are transmitted to the base station.

Offline Search Method Using Multi-Channel Reverse Link A problem that may be encountered in applying the above is the result of closed loop power control. During the period when the mobile station increases its transmit energy to compensate for the off-line period, the receiving base station will detect that the energy of the received signal is too high. In response, the base station will send a series of down commands that reduce the reverse link transmission pull-up energy early to fully compensate for the period during which the mobile station is performing an offline search. Let's go.

  In this exemplary embodiment, mobile station 850 transmits a plurality of channels including a pilot channel and at least one information channel. In the exemplary embodiment, base station 106 determines the validity of the reverse link signal transmission energy according to the received energy of the reverse link pilot signal. In the exemplary embodiment, the reason for using pilot channel energy to determine the closed loop power control command is that pilot channel energy is rate independent. Therefore, in the preferred embodiment of the present invention, the pilot channel transmission power is maintained at the level before frequency search excursion while increasing the transmission energy of at least one other channel transmitted by the mobile station.

  FIG. 8 is a functional block diagram of an exemplary embodiment of mobile station 850. The various functional block diagrams shown in FIG. 8 may not be shown in other embodiments of the present invention. The functional block diagram of FIG. 8 corresponds to an embodiment effective for operation according to a standard called TIA / EIA standard IS-95C or IS-2000. Other embodiments of the invention are valid for other standards, including the wide area CDMA (WCDMA) standard proposed by the standards bodies ETSI and ARIB. Those skilled in the art will appreciate that the widespread similarity between the reverse link modulation of the WCDMA standard and the reverse link modulation of the IS-95c standard facilitates the extension of the present invention to the WCDMA standard.

  In the exemplary embodiment of FIG. 8, the wireless communication device transmits information on multiple distinct channels that are distinguishable from each other by the short orthogonal spreading sequence described in the above-mentioned US application Ser. No. 08 / 886,604. Five separate code channels are transmitted by the wireless communication device: 1) first supplemental data channel 838, 2) pilot and power control symbol time multiplexed channel 840, 3) dedicated control channel 842, 4) second. Supplemental data channels 844 and 5) Basic channel 846. The first supplemental data channel 838 and the second supplemental data channel 844 carry digital data that exceeds the capacity of the basic channel 846, such as facsimile, multimedia applications, video, email messages, or other forms of digital data. Multiple channels 840 of pilot symbols and power control symbols are pilot symbols and power for controlling the transmission energy of the base station and base station group communicating with the mobile station 850 in order to consider coherent demodulation of the data channel by the base station. Carries control bits. The control channel 842 carries control information such as the mode of operation of the wireless communication device 850, the capability of the mobile station 850, and other necessary signal information to the base station. The basic channel 846 is used to carry basic information from the mobile station to the base station. In the case of voice transmission, the basic channel 846 carries voice data.

  Supplementary data channels 838 and 844 are encoded and processed by means not shown and supplied to modulator 826. The power control bit is supplied to the repeat generator 822. The repeat generator 822 provides a repetition of the power control bits before supplying the bits to the multiplexer (MUX) 824. In multiplexer 824, redundant power control bits are time multiplexed with pilot symbols and provided to modulator 826 via line 840.

  Message generator 812 generates the necessary control information message and provides the control message to CRC and tail bit generator 814. The CRC and tail bit generator 814 adds a series of cyclic redundancy check bits, which are parity bits used to check the accuracy of decoding in the base station, and adds a predetermined group of tail bits to the control message. Clear the decoder memory in the station reception subsystem. This message is then provided to encoder 816. Encoder 816 provides forward error correction coding on the control message. The encoded symbols are supplied to a repeat generator 820. The repeat generator repeats the encoded symbols and provides additional time diversity in transmission. Following the iterative generator, it is punctured according to a predetermined puncturing pattern by a puncturing element (PUNC) 819 to provide a predetermined number of symbols in the frame. The symbols are then provided to an interleaver 818. The interleaver rearranges the symbols according to a predetermined interleave format. Interleaved symbols are provided to modulator 826 via line 842.

  Variable rate data source 801 generates variable rate data. In the exemplary embodiment, variable rate data source 801 is a variable rate speech encoder as described in the aforementioned US Pat. No. 5,414,796. Variable rate speech encoders are prevalent in wireless communications. This increases the battery life of the wireless communication device through its use and increases the capacity of the system with minimal impact on the perceived voice quality. The Telecommunications Industry Association has componentized the most popular variable rate speech encoders into standards such as provisional standard IS-96 and provisional standard IS-733. These variable rate speech encoders encode speech signals at four possible rates called full rate, half rate, ¼ rate, and レ ー ト rate. The rate indicates the number of bits used to encode a frame of speech and varies from frame to frame. Full rate uses a predetermined maximum number of bits to encode a frame. Half rate uses 1/2 of a predetermined maximum number of bits to encode a frame. The 1/4 rate uses 1/4 of the predetermined maximum number of bits to encode the frame. The 1/8 rate uses 1/8 of the predetermined maximum number of bits to encode the frame. Variable rate data source 801 provides the encoded speech frames to CRC and tail bit generator 802. The CRC and tail bit generator 802 adds a series of cyclic redundancy check bits, which are parity bits used to check the accuracy of decoding at the base station, and also predetermined to clear the decoder memory at the base station. Are added to the control message. The frame is then supplied to encoder 804. The encoder 804 supplies a forward error correction code to the audio frame. The encoded symbols are provided to a repeat generator 808. An iterative generator 808 provides a repetition of the encoded symbols. Following the repeat generator, it is punctured by a puncturing element 809 according to a predetermined puncturing pattern to provide a predetermined number of symbols in the frame. The symbols are then supplied to interleaver 806. Interleaver 806 rearranges the symbols according to a predetermined interleaving format. Interleaved symbols are provided to modulator 826 via line 846.

  In the exemplary embodiment, modulator 826 modulates the data channel according to a code division multiple access modulation format and provides the modulated information to transmitter (TMTR) 828. TMTR 828 amplifies and filters the signal and provides the signal to antenna 832 via duplexer 830 for transmission.

  In IS-95 and cdma2000 systems, a 20 ms frame is divided into 16 equal numbers of symbols called power control groups. The power control reference is based on the fact that the base station receiving a frame for each power control group issues a power control command in response to determining the sufficiency of the reverse link signal received at the base station. ing.

  FIG. 9 is a functional block diagram of an exemplary embodiment of modulator 826 in FIG. First supplemental data channel data is provided to spreading element 952 via line 838. The spreading element 952 covers the supplemental channel data according to a predetermined spreading sequence. In the exemplary embodiment, spreading element 952 spreads the supplemental channel data using a short Walsh sequence (++-). The spread data is supplied to the relative gain element 954. A relative gain element 854 adjusts the gain of the spread supplemental channel data in relation to the pilot and power control symbol energy. The gain adjusted supplemental channel data is provided to a first summing input of summer 956. The pilot and power control multiplexed symbols are provided via line 840 to the second summing input of summer 956.

  Control channel data is provided to spreading element 958 via line 842. The spreading element 958 covers the supplemental channel data according to a predetermined spreading sequence. In the exemplary embodiment, spreading element 958 spreads the supplemental channel data using a short Walsh sequence (++++++++). The spread data is supplied to the relative gain element 960. Relative gain element 960 adjusts the gain of the spreading control channel data in relation to the pilot and power control symbol energy. The gain-adjusted control data is supplied to the third addition input of the adder 956. Summing element 956 adds the gain adjusted control data symbol, the gain adjusted supplemental channel symbol, and the time multiplexed pilot and power control symbols, and adds the sum to the first input of multiplier 972 and This is supplied to the first input of the multiplier 978.

  A second supplemental channel is provided to diffusing element 962 via line 844. The spreading element 962 covers the supplemental channel data according to a predetermined spreading sequence. In the exemplary embodiment, spreading element 962 spreads the supplemental channel data using a short Walsh sequence (++-). The spread data is provided to relative gain element 964. Relative gain element 964 adjusts the gain of the spread supplemental channel data. The gain adjusted supplemental channel data is provided to a first summing input of summer 966.

  Basic channel data is provided to spreading element 968 via line 846. The spreading element 968 covers the basic channel data according to a predetermined spreading sequence. In the exemplary embodiment, spreading element 968 spreads the basic channel data using a short Walsh sequence (++++ --- ++++ ---). The spread data is supplied to the relative gain element 970. Relative gain element 970 adjusts the gain of the spread fundamental channel data. The gain adjusted fundamental channel data is provided to the second input of summer 966.

  The adder 966 adds the gain-adjusted second supplemental channel data symbol and the basic channel data symbol, and supplies the added value to the first input of the multiplier 974 and the first input of the multiplier 976.

In the exemplary embodiment, pseudo-noise spreading with two different short PN sequences (PN _I and PN _Q ) is used to spread the data. In the exemplary embodiment, the short PN sequences PN _I and PN _{Q ′} are multiplied with a long PN code to provide additional privacy. The generation of pseudo-noise sequences is well known in the art and is described in detail in the aforementioned US Pat. No. 5,103,459. The long PN sequence is fed to the first input of multipliers 980 and 982. Short PN sequence PN _I is supplied to the second input of multiplier 980, a short PN sequence PN _Q is provided to a second input of multiplier 982.

  The resulting PN sequence from multiplier 980 is provided to each second input of multipliers 972 and 974. The resulting PN sequence from multiplier 982 is provided to each second input of multiplier 976 and multiplier 978. The product sequence from multiplier 972 is supplied to the addition input of subtractor 984. The product sequence from multiplier 974 is supplied to the first addition input of adder 986. The product sequence from the multiplier 976 is supplied to the subtraction input of the subtractor 984. The product sequence from multiplier 978 is provided to the second addition input of adder 986.

  The difference sequence from the subtractor 984 is supplied to the baseband filter 988. Baseband filter 988 performs the necessary filtering on the difference sequence and provides the filtered sequence to gain element 992. Gain element 992 adjusts the gain of the signal and provides the gain adjusted signal to upconverter 996. Upconverter 996 upconverts the gain adjusted signal according to the QPSK modulation format and provides the upconverted signal to a first input of adder 1000.

  The addition sequence from the adder 986 is supplied to the baseband filter 990. Baseband filter 990 performs the necessary filtering on the differential sequence and provides the filtered sequence to gain element 994. Gain element 994 adjusts the gain of the signal and provides the gain adjusted signal to upconverter 998. Upconverter 998 upconverts the gain adjusted signal according to the QPSK modulation format and provides the upconverted signal to the second input of adder 1000. Adder 1000 adds the two QPSK modulated signals and provides the result to transmitter 828.

As described above, when the mobile station 850 tunes to another frequency f2 to perform an inter-frequency search, the forward link symbol transmitted by the base station during the t _search period cannot be received by the mobile station. Similarly, instead of sending the t _search time period, the base station loses reverse link signals to the t _search time period.

While searching for the target frequency f2, the base station 106a will lose communication with the mobile station 850 and will not receive symbols during the _tsearch period. In order to overcome these symbol losses, the mobile station maintains the multiplexed power control command and pilot symbol channel 840 transmit power at a level prior to the offline search, while the mobile station maintains the first supplemental channel 838, the second Increase the transmission power of information channels including supplemental channel 844, control channel 842, and basic channel 846.

The quantity Δ _search depends on the duration of the search t _search , overcoming the loss of symbols during the period of t _search , so that the base station can still demodulate the frame correctly, with an additional required symbol energy with respect to the remainder of the frame. Equivalent to. The base station 106a can inform the mobile station 850 of the maximum allowable increment Δ _search in a message that instructs the mobile station to perform an inter-frequency search (eg, in “FCSM”). This value may depend on the maximum allowable interference currently determined by the base station 106a.

Returning from the offline search algorithm, the gain elements 954, 960, 964, 970 are supplied with a control signal that increases the gain of these channels by Δ _search dB. However, the transmission energy of the pilot channel is not affected. The reverse link power control commands, because they are generated in accordance with the received energy of the reverse link pilot signal, the closed loop power control commands will not respond to the supplied incremented delta _search in order to compensate for the offline search.

  In the preferred embodiment, Δsearch dB cannot increase the total transmitted power of the transmitted information channel, but the mobile station 850 cannot increase the transmission energy of the information channel due to power limitations. The mobile station 850 can respond. In the preferred embodiment, the mobile station 850 ranks the channels that are transmitting according to the importance that its reverse link transmission is not prevented. Factors considered for ranking may include the type of data transmitted, the availability of retransmission protocols, the type of forward error correction supplied, etc. Therefore, the mobile station 850 increases the transmission power of these channels according to this ranking.

  Base station 106a and mobile stations 102 and 850 can be configured to accomplish the above process. Source code for accomplishing the above process can easily be generated by those having ordinary skill in the art based on the detailed description provided herein.

  While the preferred embodiment of the invention has been illustrated and described, various modifications can be made without departing from the spirit and scope of the invention. For example, the mobile stations 102 and 850 can use the long code mask state to select a starting position within a frame to perform an inter-frequency search. Mobile stations 102 and 850 can select the randomization period so that the inter-frequency search generally does not extend beyond the frame. Randomization of search excursion positions between different mobile stations reduces reverse link interference and reduces the forward link total power requirement. Accordingly, the invention is limited only by the scope of the following claims.

  For the purpose of illustration, specific embodiments of the invention and examples for the invention have been described, but it will be understood by those skilled in the art that various equivalent variations can be made without departing from the scope of the invention. Can be made. For example, the embodiments are generally illustrated and described as being implemented by software and executed by a processor. Such software can be stored on any computer readable medium such as macro code stored on a semiconductor chip, computer readable disk, downloaded and stored from a server. The present invention can be realized equivalently in hardware like a DSP or ASIC.

  The disclosure of the present invention provided herein is not necessarily limited to the illustrated communication system described above, but can be applied to other communication systems. For example, although the present invention has generally been described as employed in a CDMA communication system 100, it is equally applicable to other digital or analog cellular communication systems. The present invention can be modified to employ aspects of the systems, circuits, various patents and standards described above, all incorporated by reference.

  These and other changes can be made to the invention from the above detailed description. In general, in the following claims, the terms should not be construed as limited to the specific embodiments disclosed in the specification and the claims. Accordingly, the invention is not limited by the disclosure and the scope should be determined entirely by the following claims.

Claims (5)

In a wireless communication system having a mobile station exchanging communication with a base station, a method for minimizing frequency search time comprising the following steps:
Tune the user station to a target frequency and collect and store signal samples from the target frequency;
Tune the user station to the original frequency and process the stored samples;
Sending the sample processing results to the base station; and while frequency search excursion is being performed, said frequency search excursion to minimize the effects of loss of forward link symbols and reverse link symbols Increase the amount of power allocated to the frame symbols for the affected information. The method of claim 1, further comprising maintaining a transmission energy of a pilot channel equivalent to a transmission energy of a pilot channel before the frequency search excursion. The method of claim 1, further comprising the following steps:
Determining whether the mobile station can increase the transmission power of the information channel to a desired degree;
When the mobile station cannot increase the transmission power of the information channel to the desired level, it selectively increases the transmission power of the information channel. The method of claim 3, wherein selectively increasing the transmission power of the information channel comprises the following steps:
Rank the channels according to the importance of having unblocked reverse link transmission; and adjust the transmission energy of the information channel according to the ranking. The method of claim 1, wherein the information channel comprises a control channel, at least one supplemental channel, and a fundamental channel.

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